This invention relates to a method and apparatus for removing particles of metal, fiberglass, etc., from solutions used in industrial or manufacturing processes and also neutralizing corrosive chemicals normally present in such solutions to permit the reuse or disposal of such solutions.
In the production of printed circuit boards and in a variety of similar manufacturing processes, the boards are etched in etching baths containing highly acidic and corrosive chemicals. Water or other fluid solutions are then used to remove etchant residue, oxides, machining chips, copper burrs and fiberglass fibers from the article. This is most commonly done in a mechanical scrubber in which rotating brushes loosen these particles which are carried off in a flow of rinse water, which also acts as a lubricant. Due to increased quality control standards in the manufacturing process and increasingly restrictive environmental and safety regulations and standards limiting the reuse and disposal of rinsing or washing solutions contaminated by chemicals, copper or other active metallic wastes or fiberglass fibers, it has become necessary to remove the optimum amount of acids, metal and fibers possible from these fluid solutions to permit their reuse and conserve water, and, in particular, to allow disposal in either private municipal sewerage systems or adjacent bodies of water.
Various methods have attempted to obtain neutralization of acids and removal of metallic and fibrous particles, the most common being similar to that used in electrostatic precipitators used as air filters to remove particulate carbon matter. For example, in the U.S. Pat. No. 2,944,952 to McMinn, Jr., oppositely charged metal plates are used to remove polymers from solution. In Wadsworth, U.S. Pat. No. 3,196,095, a complex series of parallel plates are used in the desalinization of seawater to remove solids in solution by means of opposite charges on the plates. Finally, in J. T. Candor, U.S. Pat. No. 3,687,834, oppositely charged electrodes are located near exits of a fluid conduit to create a plurality of alternately arranged non-uniform fields across the flowing fluid so that particles will enter the exits adjacent the more intense portion of the non-uniform fields.
Previous attempts to remove copper or other metals have been unsophisticated at best and have generally not been able to rapidly treat a washing solution to obtain an acceptable copper and fiber content for recycling or disposal. For example, if the washing solution is simply run over aluminum chips at a rate sufficient to meet the needs of the manufacturing process, insufficient metal is removed. If the solution is retained in a holding basin with the aluminum chips, an extremely long and inefficient retention time is required to remove a substantial amount of the metal. Previous attempts to neutralize acid etchant residues by the addition and mixing of precise amounts of chemicals have been equally time consuming and expensive, requiring constant chemical analysis, or unscientific, and do not produce an environmentally acceptable result.
Thus, the prior art attempts are not only relatively complex and expensive in manufacture or operation, but also often fail to reduce the levels of acids or metal in the solution sufficiently to allow the solution to be immediately recycled or disposed in the environment.